Kinetics of Fluorescence Decay in Er^(3+)∶YAG under 408.6 nm Excitation

The violet and green fluorescence spectra and the kinetics of fluorescence decay in Er^3＋ ：YAG crystal under 408.6 nm excitation were investigated by the time-resolved laser-induced fluorescence technique. The influence of multiphonon and energy transfer on the fluorescence decay of the ^4S3/2 rnultiplet were theoretically analyzed. A good agreement of the measured and the simulated decay curves was achieved. The continuous profile variety of the decay curves in the region from 548 to 561.2 nrn is found and it originates from the fluorescence overlap of ^2G9/2 and ^4S3/2 and the intensity ratio dominates the profile.

A New Method of Calculating Trap Depth of Rare Earth Materials

The mainly characteristic of trapping materials is the trap depth. So it is significant to calculate the trap depth for the trapping materials. A new method of calculating trap depth, which is based on energy band and using rate equations to analyze thermoluminescence, was brought forward. This method which uses the rate equations of the process and the thermoluminescence curve can replace traditional methods such as first order or second order kinetics. The trap depth of SrAl2O4：Eu^2＋ , Dy^3＋ and Sr4Al14O25：Eu^2＋ , Dy^3＋ was estimated from the glow curve. Then the numerical solution of the trap depth can be obtained. From the results of experiments and calculations, this method can accurately indicate the whole process.

Multiband emission from single β-NaYF_(4)(Yb,Er) nanoparticles at high excitation power densities and comparison to ensemble studies

Ensemble and single particle studies of the excitation power density (P)-dependent upconversion luminescence (UCL) of core and core-shell β-NaYF_(4):Yb,Er upconversion nanoparticles (UCNPs) doped with 20% Yb^(3+) and 1% or 3% Er^(^(3+)) performed over a P regime of 6 orders of magnitude reveal an increasing contribution of the emission from high energy Er^(3+) levels at P > 1 kW/cm^(2). This changes the overall emission color from initially green over yellow to white. While initially the green and with increasing P the red emission dominate in ensemble measurements at P < 1 kW/cm^(2), the increasing population of higher Er^(^(3+)) energy levels by multiphotonic processes at higher P in single particle studies results in a multitude of emission bands in the ultraviolet/visible/near infrared (UV/vis/NIR) accompanied by a decreased contribution of the red luminescence. Based upon a thorough analysis of the P-dependence of UCL, the emission bands activated at high P were grouped and assigned to 2–3, 3–4, and 4 photonic processes involving energy transfer (ET), excited-state absorption (ESA), cross-relaxation (CR), back energy transfer (BET), and non-radiative relaxation processes (nRP). This underlines the P-tunability of UCNP brightness and color and highlights the potential of P-dependent measurements for mechanistic studies required to manifest the population pathways of the different Er^(3+) levels.